The present invention relates generally to laser cutting machine tools and is particularly directed to laser cutters of the type which cut patterns in sheet material under the control of a programmable logic controller or a computer numerical controller. The invention is specifically disclosed as a xe2x80x9chead-downxe2x80x9d laser cutter in which the movements of the laser head are pre-determined so as to not pass over an area of the material that has already been cut, thereby eliminating any head-up/head-down laser head movements that would otherwise be necessary, while at the same time minimizing the rapid-travel distance of the laser head to make all required cuts.
Laser cutting tools have been available for years which have the capability of cutting through various material types and thicknesses, typically utilizing a piece of sheet stock material. Conventional laser cutters, such as the Model CL-5 CNC Laser Center, manufactured by Cincinnati Incorporated, typically have a laser head assembly that moves in one direction with an attached laser head that moves in the perpendicular direction. Such conventional laser cutters are typically controlled by a sophisticated computer numeric controller (CNC), which operates according to a group of instructions called xe2x80x9cNC codexe2x80x9d which is a specific set of instructions for determining the cutting pattern that creates a series of shapes out of a sheet of material. Conventional laser cutters are usually powerful enough to cut through metal materials, including aluminum and steel, and in some cases, the thickness of such metal materials can be as great as one-half inch.
To properly utilize a laser cutter, a computer-aided design file (i.e., a xe2x80x9cCADxe2x80x9d-file) is created to define the shapes of all of the parts that are to be made from a single sheet of material. In many cases, such parts are repeated several times in one sheet of material, however, using the technology available today, parts having several different sizes and shapes can all be made out of one sheet of material, and the creator of the CAD-file normally attempts to obtain as many parts as possible from a single sheet of material.
The CAD-file is typically in the form of an xe2x80x9cIGESxe2x80x9d (Initial Graphics Exchange Specification) or xe2x80x9cDXFxe2x80x9d (Drawing Interchange File) format, which are industry standards used in the computer-aided drafting industry. After a pattern has been created for one particular part, this pattern can be either replicated, or added to other patterns that create parts having other sizes and/or shapes. This process of placing several different parts to be cut from one sheet of material is known as xe2x80x9cnesting.xe2x80x9d Once the CAD-file (in either an IGES or DXF format) has been prepared for the entire sheet of material to be cut by the laser head, the CAD-file is further processed to generate xe2x80x9cNC code,xe2x80x9d which now generates the necessary commands to control the movements of the laser head to perform the actual cutting operations needed to create the physical parts from the sheet material.
The step of generating NC code is often referred to as xe2x80x9cpost-processing.xe2x80x9d This terminology is sometimes used to refer to the fact that the CAD-file for the entire sheet material has already been completely created, however, further manipulations or xe2x80x9cprocessingxe2x80x9d must be performed to add special command codes that cause the laser head to actually perform the movements necessary in the cutting operations. This NC code is also sometimes referred to as a xe2x80x9cpart program,xe2x80x9d and typically utilizes computer software provided by companies known as xe2x80x9cCAD/CAM vendors.xe2x80x9d Examples of CAD/CAM vendors are: Optimation, located in Independence, Mo.; Measurement Masters, located in California; Metalsoft, located in California; Teksoft, located in Phoenix, Ariz.; and Merry Mechanization, located in Florida.
When a CAD/CAM vendor creates a software product that creates NC code, the CAD/CAM vendor typically must make such software product to be compatible with a specific manufacturer of laser cutters, such as Cincinnati, Incorporated. The act of creating the NC code is quite sophisticated, because the CAD/CAM software must scan the entire CAD-file to determine what cuts must be made in the sheet of material. To optimize the use of the laser cutter, the CAD/CAM software will typically attempt to discover the quickest way to move the laser head to perform all of the necessary cuts. Such head movements can include very fast X-Y movements (also known as xe2x80x9crapid-travelxe2x80x9d movements), either with the head in its xe2x80x9cupxe2x80x9d position or its xe2x80x9cdownxe2x80x9d position. In addition, the movements of the laser head must be controlled at a standard xe2x80x9ccutting rate,xe2x80x9d which is the velocity at which the laser head moves parallel to the top surface of the sheet material while making a cut with the laser beam turned on. Each laser cutter typically will have a different cutting velocity for different types of materials and for different material thicknesses. As is well known in the art, the laser cutter cannot effectively be moved faster than the time required for the laser beam to cut entirely through the thickness of the material at each incremental distance along the surface of the sheet material.
Conventional CAD/CAM software products attempt to minimize the amount of time that the laser head is moving in a fast-travel mode, because this essentially is the mode that can be most easily manipulated. The slower cutting velocity mode cannot be easily increased so as to decrease the total amount of time needed to make all of the cuts, because the laser head must literally make every cut in the sheet material at a certain rate before the step of cutting is completed. It is possible to vary xe2x80x9clead-inxe2x80x9d movements to minimize the (slower) cutting velocity mode cumulative time, however, the great proportion of time in this cutting mode is spent actually making the cuts. Therefore, the most significant amount of time that may be saved is in the faster (xe2x80x9crapidxe2x80x9d) travel mode, and in the number of head-up/head-down movements of the laser head.
Head-up/head-down movements are typically required in conventional laser cutters so that the laser head can pass over an area of the sheet material that already has had a part previously cut without colliding with any skewed parts. As can be seen in FIG. 2, if a relatively large portion of the sheet material is cut out, it may not be able to completely fall down onto the machine bed, and therefore, may have a portion that extends above the plane in which the tip of the laser head operates. The laser head can easily be damaged if it is allowed to impact against a piece of material that protrudes above the planar surface of the sheet material being cut, and such damage can be very expensive because of the high price of laser cutting heads. In addition, it is desirable for the laser head to also avoid previously cut areas where a relatively large cut-out has been made, to prevent a non-contact laser head from xe2x80x9cdivingxe2x80x9d into this large open area, and to prevent the head from impacting against the internal edge of this cut-out.
Accordingly, it is a primary object of the present invention to create a special part program comprising NC code that optimizes the high-speed rapid-travel movements of a laser cutting head used in cutting sheet material, while eliminating all head-up/head-down movements of the laser head.
It is another object of the present invention to create an optimized part program comprising NC code that inspects multiple ways of sweeping through the necessary cuts defined in the CAD-file to determine the minimum amount of high-speed rapid-travel of the laser cutting head used in cutting sheet material, while eliminating all head-up/head-down movements of the laser head.
It is a further object of the present invention to create an optimized part program comprising NC code that manipulates the angle and placement of lead-ins for each of the cut-outs to be made in a sheet material, so as to minimize the amount of rapid-travel distance required by the laser cutting head while performing the cutting operations.
It is yet another object of the present invention to create a part program comprising NC code that minimizes the amount of high-speed travel of the laser cutting head used in cutting sheet material, and also minimizes the number of head-up/head-down movements of the laser cutting head while performing the cutting operations.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention.
To achieve the foregoing and other objects, and in accordance with one aspect of the present invention, an improved laser cutting apparatus is provided that optimizes the amount of time required to perform all of the required cuts in a piece of sheet material, in which the optimization minimizes the amount of rapid-travel movement of the laser head, and virtually eliminates all head-up/head-down movements of the laser head. In one embodiment, the present invention accepts NC code that has already been created by a conventional software product produced by a CAD/CAM vendor, and analyzes that NC code to create an optimized part program. In this first embodiment, the NC code is broken down and analyzed as a series of individual shapes to be cut by the laser head. Once the required shapes are known, the present invention performs a xe2x80x9csweepxe2x80x9d to determine how many cut-outs are in each xe2x80x9cbandxe2x80x9d being analyzed across the surface of the sheet material to be cut. The number of bands and the types of sweep are varied to analyze different possibilities of rapid-travel distance while still eliminating all head-up/head-down movements of the laser head. As a refinement, the first embodiment analyzes the order in which the cut-outs are to be cut within a particular band, and also determines the placement and direction of the lead-in for each of the cut-outs. This is all done for each xe2x80x9csweep-typexe2x80x9d and for each number of bands so as to calculate the rapid-travel distance for each possibility, thereby determining the minimum rapid-travel distance possible for the particular series of cut-outs to be made on this sheet material.
Since the ultimate goal is to minimize the amount of rapid-travel distance, and thereby minimize the amount of time required to make all of the required cuts in the sheet material, the present invention repeatedly selects a type of xe2x80x9csweepxe2x80x9d and a given number of xe2x80x9cbandsxe2x80x9d to repeatedly analyze the order in which the cut-outs would be made. After each analysis has occurred, the rapid-travel distance is stored so as to be compared against later calculations for that same quantity. Assuming a particular type of sweep, the number of bands initially is typically set to a value of one (1) band for the initial analysis step. Another analysis step is performed after incrementing the number of bands, and further analysis steps are performed up through a maximum number of bands typically in the range of twenty (20) to thirty (30). This incrementing the number of bands is preferably performed for each sweep type, before making the final determination as to the minimum rapid-travel distance. After each sweep has taken place for a particular number of bands, if the most recent cumulative rapid-travel distance is less than that previously stored, then that particular part program is stored as the provisional xe2x80x9cbestxe2x80x9d possibility with regard to minimum cutting times.
In the first embodiment, only possibilities that require no head-up/head-down movements of the laser head are considered. In a second embodiment, if it is impossible to find any solutions that provide zero head-up/head-down movements, then the present invention will perform all of the calculations related above while allowing at least one head-up/head-down movement to be included in the part program. In this second embodiment, the present invention will determine not only the minimum rapid-travel distance, but especially the minimum number of head-up/head-down movements that would be needed to perform all of the required cut-outs in the sheet material.
In all embodiments, it is preferred that more than one sweep type be considered when analyzing the minimum cumulative rapid-travel distance. Examples of sweep types include: (1) X-sweep, (2) Y-sweep, (3) Radial Wave, inside-out (using concentric circles), (4) Radial Wave, outside-in, and (5) Radial Pie.